Heat dissipation is becoming an increasingly important issue for mobile power amplifiers. The requirement for better thermal conduction is partly due to shrinking power amplifier die and package sizes, which increases the demands simply by increasing the thermal densities. In addition, modern mobile amplifiers typically operate at higher data rates, and closer to peak output powers on average. Moreover, the increased multi-band capabilities of modern mobile amplifier modules generally means that the amplifier must overcome greater series insertion loss to the antenna (in the form of increased, switch and filter content), which also increases the power demand on the amplifier.
The thermal resistances of materials m a structure impact the ability to dissipate heat. According to a known amplifier structure, minimum values for thermal resistance are obtained when the power amplifier die thickness is minimized, or when the output area occupied by the power transistor is increased. Both of these factors are undesirable from a practical point of view. For example, minimizing the power amplifier die thickness increases yield loss problems associated with thin wafer handling and breakage, and also increases yield loss problems associated with thin die pick and place in packaging. Also, increasing the output area occupied by the power transistor increases the overall power amplifier die area, which consequently increases the cost of the power amplifier die and the overall package size. In practice, lower cost power amplifier die and smaller overall package sizes are highly desirable.
What is needed, therefore, is an apparatus that overcomes at least the shortcomings described above.